1. Field of the Invention
The present invention is related to mobile networking and, more particularly, to mobile networking using the Mobile IP standard.
2. Description of the Related Art
Advances in wireless communication technology have given rise to a number of wireless applications such as pagers, cellular phones, and mobile computing and networking applications. Mobile computing and networking allows a mobile device capable of connecting to a network to freely move while remaining connected to the network and to the Internet. As the mobile device moves between different networks and sub-networks, the connection to the old network or sub-network is dropped as needed, and a connection to a new network or sub-network is established. Such a handoff is made possible through an extension of the Internet Protocol (IP) referred to as Mobile IP. In general, Mobile IP creates the perception that the mobile device is always attached to the same network or sub-network even as it is moving around. Specifically, Mobile IP allows the mobile device to retain the same network or IP address regardless of the particular network or sub-network to which the mobile device is actually connected. Thus, a remote application can send data packets to the mobile device at the same IP address no matter how many handoffs (i.e., changes in network or sub-network connections) may have occurred.
Mobile IP accomplishes the above function by allowing the mobile node to use two IP addresses. The first IP address, called the home address, is static and is used to identify the mobile device when it is in its home network. A home network is the network in which the mobile device appears to be located for the rest of the network or the Internet. More formally, the home network is the network which contains the home registration of the mobile device. The second IP address, called the care-of address, is dynamic and is used to identify the mobile device when it is away from the home network. As the mobile device is handed off to each new network or sub-network, it obtains a care-of address from that network or sub-network. The mobile device is likely to use multiple different care-of addresses as it roams between different networks and sub-networks. Upon obtaining a new care-of address, the mobile device registers the new care-of address with the home network. Thereafter, the home network redirects data packets that are destined for the mobile device at its home address (in the home network) to the new care-of address.
Although Mobile IP allows the mobile device to freely move between different networks and sub-networks while appearing to maintain the same network connection, the transition is not always a seamless one. For example, when a handoff occurs in the middle of an ongoing data transfer session, some data packets may be sent to the old care-of address before registration of the new care-of address can be completed. As a result, these data packets may become lost, thereby disrupting the flow of data packets to the mobile device. Depending on the duration of the disruption, the data transfer session may be only slightly affected or severely affected. For example, where the network is particularly slow or congested (hence, registration is delayed), a large number of data packets may be lost, possibly causing the application session to terminate or otherwise fail.
Accordingly, it is desirable in a wireless access network to provide a system and method for handing off a mobile device in a substantially seamless manner.